In previous studies from this and other laboratories, the MDCK dog kidney epithelial cell line has been shown to: (a) form continous epithelial cell sheets when grown in vitro, (b) regenerate kidney tubular-like structures in vivo, (c) transport salt and fluid from mucosal to serosal suface by a mechanism which is responsive to cyclic AMP, (d) possess adenylate cyclase activity which is responsive to vasopressin and other hormonal agents, and (e) possess a saturable Na ion transport system which functions independently of energy and is insensitive to oubain inhibition. We wish to continue our studies on the MDCK cells in order to better understand: (a) the differentiated kidney sppcific transport properties of the MDCK line, and (b) the factors regulating the growth and polarity properties of these cells. Our goals are to: 1. Further establish the differentiated transport and regulatory properties of the MDCK cells. 2. Employ the newly developed serum free growth medium to determine the factors and conditions required for maximal expression of kidney specific biochemical traits. 3. Quantitate the changes in the differentiated properties which accompany neoplastic transformation of the MDCK cells. 4. Determine the changes in in vitro growth requirements which accompany transformation. 5. Establish a causal relationship between modification of in vitro growth dependency and transformation to the cancerous state.